The present invention relates to an add-on child restraint system for the protection of a child occupant placed in a motor vehicle and more particularly to a forward facing child car seat providing superior safety performance.
Passenger restraint systems of motor vehicles provide adequate protection for adult passengers, but are inappropriately sized for small children. As a result, regulations have issued requiring the use of child restraint systems in motor vehicles. The regulations impose size, shape and mechanical performance requirements on child restraint system manufacturers to ensure that the restraint system is capable of safely securing the child in a variety of vehicle passenger seats during operation of the motor vehicle and, in particular, during periods of worst-case rapid vehicle deceleration events (e.g., hard braking or forward impact events). In recent years, more stringent requirements have been adopted for child restraint systems in response to continued incidents of injuries sustained by children due to faulty or inappropriately designed restraint systems. In particular, regulatory requirements in Canada, the United States, and the European Union governing the use of add-on child restraint systems (i.e., portable child car seats) in motor vehicles require that the restraint system must be capable of limiting passenger excursions during a simulated vehicle frontal impact event, as defined under the restraint system dynamic tests of the United States Federal Motor Vehicle Safety Standard No. 213 (FMVSS 213), the Canadian Motor Vehicle Safety Standard No. 213 (CMVSS 213) and the Uniform Provisions Concerning the Approval of Restraining Devices for Child Occupants of Power-Driven Vehicles (ECE R44.03, xc2xa78.1.3).
The impact test setup, procedure and test article performance requirements under FMVSS 213 and CMVSS 213 are defined in terms of the restraint system""s intended use (i.e., forward or rearward facing restraint or a built-in restraint system) and the recommended passenger weight ranges (which is related to passenger size) since the adequacy of the restraint system during a forward impact varies depending on the passenger weight, size and position in the vehicle seat.
Forward Facing Add-on Restraint Systems
In the case of a forward facing add-on restraint system, test procedures distinguish between two categories of restraint systems: forward facing child restraints with harness and belt positioning booster seats. In the case of forward facing child restraints with harness, the car seat body includes a child restraint harness and a vehicle seat belt retention device (or seat belt pathway) for restraining the seat in the vehicle seat. In the case of belt positioning booster seats, the vehicle manufacturer supplied seat belt assembly is used to restrain the child and booster seat in the vehicle seat.
FMVSS 213 and CMVSS 213 require that the restraint system with harness must be capable of being fully restrained (as verified by the forward impact test) in the vehicle seat by a Type I seat belt assembly (lap belt only), or by the combination of a Type I seat belt assembly and a top tether secured to a vehicle supplied anchorage which is often located in the vehicle seat assembly rear filler panel. The Type I seat belt assembly restraint requirement for forward facing child restraints with harness is intended to ensure that the restraint system will perform adequately whether the vehicle seat comes equipped with either a Type I or Type II (lap and shoulder belt) seat belt assembly.
Impact Test Setup, Procedure and Performance Requirements
Under FMVSS 213 and CMVSS 213, the testing platform comprises a vehicle seat assembly mounted on an impact trolley subjected to a change in velocity by impact with a frontal barrier or an equivalent rearward acceleration of the trolley simulating the acceleration experienced during a forward impact. The standard seat assembly for the impact test is reproduced as FIG. 1A. The impact test setup, procedure and data gathering for forward facing add-on child restraints will now be briefly described. The restraint system with an anthropomorphic test dummy is secured in the vehicle seat using the seat belt assembly mandated for the test (i.e., Type I seat belt assembly) and subjected to the forward impact loads. In addition to verifying the strength of the restraint system, the impact test is used to gather data on the acceleration and displacement of the test dummy during the impact test. This procedure is repeated for a variety of test dummy weights and sizes, depending on the recommended weights for the child restraint. For example, conventional forward facing child restraints with harness are usually recommended for use with children weighing between 22 and 40 lb. For this type of restraint, an impact test is required for both a test dummy simulating 9 month old, 20 lb. child and 3 year old, 33 lb. child. For seats recommended for children weighing between 40 and 50 lb., the impact test is required for a test dummy simulating a 6 year old, 48 lb. child. Neither FMVSS 213 nor CMVSS 213 regulate child restraints for passenger weights over 50 lb.
The limits set forth in the regulations are defined in terms of a maximum allowable forward dynamic displacements and accelerations of the test dummy, as measured during the impact test. Maximum allowable accelerations of the test dummy are defined in terms of maximum measured accelerations of the head and upper thorax. Maximum allowable forward displacements (or excursions) of the test dummy are measured at the head and either knee joint portions of the test dummy and are measured with respect to a seatback pivot axis (15) of the standard seat assembly (17), as illustrated in FIG. 1A. FMVSS 213 require that neither the head nor the knee joint of the test dummy can exhibit a forward excursion during test exceeding a maximum excursion distance (L), which represents the distance between seatback pivot axis (15) and an imaginary plane (10) disposed in front of standard seatback assemble (10). Currently, FMVSS 213 imposes a forward excursion limit (L) of the test dummy head and either knee joint to 813 mm and 915 mm, respectively. Under CMVSS 213, the forward excursion limit (10) for the head is 720 mm (excursions of the kneejoint are not regulated in Canada).
The forward facing child restraint excursion limits and seat belt assembly restraint requirements under FMVSS 213 and CMVSS 213 require child car seat manufacturers to design restraint systems that must be capable not only of sustaining forward impact loads imposed during the impact test, but must also be capable of preventing the passenger and seat from exceeding the maximum allowable forward excursion (L). At present, there are no known forward facing add-on child restraints with harness that meet the forward excursion limit requirements of FMVSS 213 or CMVSS 213 for passenger weights above 40 lb. Moreover, there are no known child restraints with harness available that meet the requirements under FMVSS 213 or CMVSS 213 for weights ranging between 22 and 40 lb. without the use of an additional restraining top tether.
The Loading Environment During a Forward Impact
The ability of a particular child restraint system to meet the excursion limits requirements depends not only on the strength and/or stiffness properties of the restraint system, but also on the nature of the load environment during a forward impact event. During a forward impact, the conventional forward facing child restraint with harness is subjected to both an applied lateral load through the vehicle seat belt assembly and a forward tipping moment. The forward tipping moment is influenced primarily by the vehicle seat belt/child seat shoulder harness force couple carried by the car seat body. Since the lap belt restraint force applied to the car seat is not co-linear with the inertia load applied to the shoulder harness restraint, there is a resulting forward tipping moment applied to the child car seat proportional to the distance between the line of actions of the vehicle seatbelt and child seat shoulder harness applied loads. If a top tether in combination with a Type I set belt assembly is used, this tipping moment is minimal since the top tether line of action is approximately co-linear or above the shoulder restraint (thereby minimizing the total moment arm). However, if a top tether is not used or the vehicle is not equipped with an anchorage for the top tether, this tipping moment can be quite severe.
Drawbacks and Limitations of Known Child Restraint Systems
While it is usually the case that a child restraint system is capable of sustaining lateral loads during a forward impact, it has been found that the most serious of injuries sustained by children secured in forward facing child restraints usually result from a head contact resulting from a failure to adequately limit the forward motion (excursion) of the head. While it is known that tipping moments need to be taken into account in child car seat designs, many of the present day child car seats are not designed with a view towards optimally minimizing the effects of a forward tipping.
One cause of child restraints allowing excessive forward head excursions occurs when the vehicle seatbelt restraint system has a seatbelt anchor positioned forward of the seatbelt entry point for a child car seat placed in the vehicle seat. When the seatbelt anchor is positioned forward of the seatbelt entry, it is difficult to tension the seatbelt against the child car seat in order to ensure that the car seat fits snugly against the vehicle seat (as discussed in detail in the background section of U.S. application Ser. No.: 08/738,052, the disclosure of which is expressly incorporated herein by reference). In an effort to promote compatibility between a child restraint system and vehicle seat belts, the SAE (Society of Automotive Engineers) publishes voluntary design guidelines defining recommended seat belt entry positions for car seats. In particular, SAE Standard J1819 sets a maximum forward buckle stalk length of 200 mm from the seat bight (the intersection of the vehicle seat back and the seat bottom or pan) and recommends that the child restraint system adopt a seat belt entry position outside this 200 mm radius. By placing the seat belt entry position outside of this 200 mm radius, the seat belt can be effectively tensioned against the child car seat to ensure a snug fit in the vehicle seat and thereby minimize the instances of car seats becoming dislodged from the vehicle seat belt when subjected to the forward tipping moment. SAE Standard J1819 also establishes a standard vehicle seatbelt length (approximately 41 in) to insure that the vehicle seatbelt has a sufficient length to be passed through the belt pathway of child restraint when buckled. It is therefore preferable to provide a seat belt entry position outside this 200 mm radius for child car seats to ensue that the child car seat can be fit snugly in the vehicle seat and a seatbelt pathway that can receive a vehicle seatbelt having a maximum seatbelt length of 41 inches.
In addition to the need for complying with the standards under SAE J1819, there is the additional need to provide a child car seat design which is effective in limiting the forward excursions of the child car seat and in maximizing the distance between the passenger and the forward excursion limit under CMVSS 213 and/or FMVSS 213. The known child restraint designs do not provide optimal performance. Often, child restraints represent compromises in which non-safety related features (such as providing an elevated seating position) reduce performance. An elevated seating position increases the moment inducing forces tending to rotate or tip the child car seat forwardly during a forward impact event.
Typical child restraint designs have a child seating surface that is positioned substantially forward of the vehicle seat back (thereby reducing the amount of allowable forward excursion before a head strike would occur). One of the primary causes for positioning the child seating surface substantially forward of the vehicle seatback is to give ample clearance for the child harness behind the child car seat. Typical child restraint designs will also have a seat belt entry point that is not positioned forward of the vehicle seat belt anchor position (thereby making it difficult to properly restrain the child car seat in the vehicle seat using a vehicle seatbelt) or is positioned in such a manner as to induce a severe tipping moment. For example, U.S. Pat. No. 4,033,622 to Boudreau describes a child restraint including a seat body shell supported by tubular steel frame having a seat belt entry positioned adjacent to the vehicle lower seat. The performance of Boudreau""s car seat is sub-optimal for several reasons. First, the seat belt entry position is positioned well below the child shoulder harness restraint, thereby subjecting the car seat to a large tipping moment during a forward impact. As mentioned above, when the vertical distance between the child shoulder restraint and the seat belt pathway is substantial, the magnitude of the applied moment is correspondingly increased. Second, the position of the seat belt entry point does not meet the standards set forth in SAE J1819 (i.e., the entry point is not outside the 200 mm radius from the seat bight).
Some child restraints are designed to be effective in reacting the tipping moment, but rely on a vehicle shoulder harness for minimizing forward excursions. As such, these restraints provide a sub-optimal child restraint when used in vehicles which provide only a lap belt restraint (a Type I seatbelt). For example, U.S. Pat No. 4,826,246 to Meeker describes a child car seat with harness that is designed with a view towards reducing the tipping moment when the car seat is secured in a vehicle seat using a three-point vehicle seat belt assembly (a Type II seatbelt). An additional drawback of Meeker is that the child seating surface is offset from the vehicle seat back to accommodate the tubular frame for receiving the seat belt and supporting the seat (as with Boudreau).
Some child restraints provide for a child seat that is positioned flush against the vehicle seat back (thereby minimizing the forward offset from the vehicle seat), but require additional restraint devices for securing the child seat in the vehicle seat. One example of such a restraint device is disclosed in U.S. Pat. No. 3,910,634 to Morris, which relies a top tether system, thereby requiring the vehicle to provide anchorage points for both the seat back and seat bottom anchorage straps to provide an adequate restraint for the seat. Although car seats with harness that use a top tether restraint (as in Morris) are effective in reducing the effects of a tipping moment, this approach is disfavored for two reasons. First, users will often disregard attaching the top tether and simply secure the child seat using only the vehicle seatbelt. Second, in the U.S., very few vehicles are equipped with a top tether anchor, thereby requiring the user to install an anchor in the vehicle in order to properly restrain the child seat in the vehicle seat. Another example of an additional restraint device is illustrated in U.S. Pat. No. 3,709,558 to Jakob. This child restraint provides a seat body adapted to be placed flush against the vehicle seat. However, the seat belt restraint used in Jakob is limited to use in vehicles that have seat belt anchors that do not extend beyond the seat bight. Jakob""s seat belt restraint is therefore disfavored since the restraint does not comply with the compatibility standards under SAE J1819.
Some child restraint designs are equipped with seatbelt entry points that are positioned away from the vehicle seat bight (thereby being more readily adapted for compliance with the recommended seatbelt anchor position under SAE J1819), but will contain inherent shortcomings in the seatbelt routing path affecting the strength performance of the child car seat during a forward impact event. For example, U.S. Pat. No. 4,345,791 to Bryans discloses a child restraint that positions the vehicle seatbelt over the front side wall surfaces of the seat and across the seating surface. Bryans""s child restraint is disfavored since by extending the vehicle seatbelt across the seating area, the seatbelt will apply an inwardly directed resultant force at the side wall restraint points tending to buckle the seat during a forward impact event. It is preferable to rout the vehicle seatbelt in such a way as to eliminate any net inwardly directed forces applied to the child seat. Another example of a child restraint having a vehicle seatbelt pathway extending across the seating area is found in U.S. Pat. No. 4,040,664 to Tanaka.
In light of the drawbacks and limitations described and shown in existing forward facing add-on child restraint systems, there is a need for a child restraint that provides superior safety performance during a vehicle forward impact event. In particular, the known child restraints suffer from one or more of the following drawbacks: the vertical seat back of the child car seat is offset from the vehicle seat back, thereby reducing the distance between the child occupant and a forward interior obstacle of the vehicle; the seating surface for the child is elevated and/or the position the seat belt pathway is positioned too low in the seat, either of which can make the child car seat susceptible to excessive tipping during the forward impact event; the child car seat relies on a tubular frame or other similar type of strengthening structure disposed between the child seating surface and the vehicle seat to react applied loads, thereby preventing the child seating surface from being positionable in close proximity to the vehicle seating surface so as to increase the distance between the child occupant and a forward interior surface of the vehicle; or the child car seat requires the use of a top tether anchorage or vehicle shoulder belt to effectively restrain the child car seat in the vehicle seat.
The invention satisfies these needs while avoiding the problems and disadvantages of the existing art by providing a forward facing child restraint with harness that exhibits a high degree of flexural rigidity during a forward impact event, positions the seating surfaces for the child occupant in close proximity to the vehicle seating surfaces, and is fully restrainable in a vehicle seat using only a vehicle lap belt (i.e., a Type I seatbelt restraint). In particular, the child restraint system of the invention is readily adapted for meeting the safety requirements of CMVSS 213 and FMVSS 213 for passenger weights ranging from 20 to 60 lb. for a Type I seatbelt restraint without a top tether anchorage, and also meets seatbelt compatibility standards under SAE J 1819.
In one aspect of the invention, the child restraint includes a seating portion formed integrally with a vehicle seatbelt pathway for fully restraining the child car seat using only a vehicle lap belt. The seatbelt pathway includes left and right seatbelt restraints disposed on left and right triangularly shaped supports formed with the seat portion, and a central pathway extending across the rear surface of the upper seatback of the seating portion. Each of the vehicle seatbelt restraints are formed on a diagonal member of the triangularly shaped support extending between an upper and lower end of the car seat.
Preferably, the diagonal member includes a bend formed adjacent to the seatbelt restraint surface for locating and visual identification of the seatbelt restraint surface on the diagonal member. The bend also serves as a preferred approach for reducing the seatbelt pathway length to accommodate seatbelt lengths adopting the standards set forth under SAE J1819. Each of the triangularly shaped supports may also include a support member orientated to extend along the line of action of the forces applied at the seatbelt restraint surfaces by the vehicle lap belt, and a lower transverse member extending between the left and right support members of the respective left and right triangular supports. The support members and lower transverse member are operative for providing additional strength and/or stiffness to the child car seat when seatbelt loads are applied at the seatbelt restraint surfaces.
In a further aspect of the invention, the child restraint includes a support frame having left and right supports coupled to the left and right sides of an L-shaped seat portion. Child harness and vehicle seatbelt restraint loads are transmitted directly to the support frame by restraining the vehicle seatbelt against restraint surfaces formed on the left and right supports and anchoring the child harness to the support frame. The left and right supports function as the primary load paths for loads induced during the forward impact event. The left and right supports include a primary strut extending downward from a top end proximal to the upper end of the seat portion and terminating at a front end proximal to the forward end of the seating portion, a central portion disposed between the top and forward ends, and an axial strut coupled to the central portion and to the seat portion adjacent to the seat portion apex, defined as the location where the horizontal and upstanding seatback of the seat portion meet. In this embodiment of the child restraint, the support frame and seat portion may be implemented as a network of tubular bars coupled to a seat panel, or the support frame and seat portion may be constructed as a one-piece car seat shell.
In the tubular bar implementation of the child restraint, the axial strut corresponds to an axial bar and the primary strut corresponds to a diagonal bar interconnected by, for example, a weld joint. The left and right supports may also include an L-shaped bar section connecting the seat panel to the axial bar and diagonal bar. In this configuration, the bar frame defined by the L-shaped bar and diagonal bar describes a triangularly shaped support structure providing a high degree of flexural rigidity to the child car seat when the child car seat is subjected to a forward impact event.
In the shell implementation of the child restraint, the left and right supports correspond to walls of a load-bearing shell structure wherein the axial strut corresponds to stiffeners formed integrally with an outer wall section and the primary strut corresponds to a diagonally extending wall section. The left and right supports may also include an L-shaped section connecting the seat portion to the integrally formed stiffeners and the diagonally extending wall section. In this configuration, the shell defined by the L-shaped section and diagonally extending wall section describe a triangularly shaped shell structure providing a high degree of flexural rigidity to the child car seat when the child car seat is subjected to a forward impact event, as was found in the case of the tubular truss implementation. Thus, the child restraint system of the invention may be practiced by a network of bars with attached seat panel or by a car seat shell structure.
In still another aspect of the invention, there is provided a shell structure of a child car seat characterized as a semi-monocoque shell. The semi-monocoque shell is a closed walled, load bearing shell having a top end defining shoulder strap restraint points of an attached child harness, a forward end, a seat portion formed between the top and forward ends of the seat portion, and left and right frame portions defining left and right vehicle seatbelt restraint surfaces extending forwardly from the seat portion. The left and right frame portions are adapted for reacting a substantial portion of the forward inertia loads applied at the child harness restraint points and rearward restraint loads applied by the vehicle lap belt during the forward impact event. Thus, the left and right frame portions are adapted for providing a majority of the bending stiffness to the child restraint for limiting forward excursions during the forward impact event.
The seat portion of the semi-monocoque shell includes a vertically disposed pair of front and rear panels of a vertical seat portion defining a front seating surface and rear surface positionable against the vehicle back support surface, respectively, and a horizontally disposed pair of front and rear panels of a horizontal seat portion defining a front seating surface and rear surface positionable against the vehicle seat bench, respectively. The front and rear panels of the vertical seat portion are positioned in such a manner as to provide an upper seating surface disposed in close proximity to the vehicle back support surface at the vertical seat portion""s upper end. The front and rear panels of the horizontal seat portion are positioned in such a manner as to provide a lower seating surface disposed in close proximity to the vehicle seat bench at the horizontal seat portion""s rearward end. Preferably, the front and rear planar panel portions of the horizontal seat portion include an integrally formed stiffener for strengthening the seat. The stiffener may be formed by an inwardly protruding series of tac-offs formed on the front panel and extending through and structurally coupled to the rear panel, or by inwardly protruding rib stiffeners formed on the rear panel. In either case, the thickness of the horizontal seat section is determined by the desired size of the tac-offs, rib stiffeners, or a combination thereof.